The invention accordingly relates generally to voice transmission systems in which the pressure fluctuations induced by speech are first converted to an electrical signal by a transducer, transmitted through a pair of wires, and resolved into audible sound by means of a solenoid -- through which the transmitted electrical signal is caused to pass -- acting upon a flexible membrane.
The invention relates more particularly to devices in which the transmitted signal is a train of pulses of similar amplitude.
Sound transmitting devices of the prior art do not, in general, operate in this manner. Most commonly the transmitted signal corresponding to a continuously varying sound input is an analogous, continuously varying voltage.
Where transmission occurs in a pulsating current -- as in Pulse Code Modulated telephone transmission -- the receiver and speaker still operate on continuously varying signals, the PCM encoder and decoder being interposed between the ultimate terminals.
It is a primary object of the invention to provide a voice-grade transmission system in which the sound input is converted directly into a pulsed current, transmitted as such through a pair of wires, and resolved into coherent speech at the receiver.
It is a further object of the invention to provide a transmission system requiring no electronic components and operating entirely in a telegraphic mode from a direct-current power source.
It is yet another object of the invention to provide a telegraphic voice transmission system of relative structural simplicity, one which is economical in manufacture, reliable in operation and one which is easy to operate or use.